The chronic, spastic cough started with what appeared to be a cold. A few months later, it was ruining Zachary Graham’s life. The 16-year-old Sunapee, N.H., resident was often left gasping for air, gagging and unable to sleep. During one particularly ghastly coughing spell, Betty May Graham, Zachary’s mom, feared her son was about to stop breathing.

That incident led the family to a lung specialist who delivered a diagnosis that stunned the Grahams: Zachary had pertussis, also known as whooping cough, a disease far better known in the 1930s than today.

“When the doctor said whooping cough, it kind of blew my mind,” the teenager says.

Adds his mother: “I had never heard of an adolescent having whooping cough. I thought, ‘He had his shots for that; how could he get whooping cough?’ ”

They’ve found that the pertussis vaccine routinely administered to babies wears off in five to 10 years. As a result, a disease that was thought to be a relic of the past has re-emerged and is finding fresh targets — primarily teenagers and young adults.

Pertussis ran rampant in the early part of the 20th century, with around 250,000 cases — and about 7,500 child deaths — reported each year in the U.S.

A highly contagious bacterial infection that causes severe coughing, the disease derives its common name from the “whoop” sound that infected infants make as they struggle to breathe while coughing. The infection often resembles a cold in its early stages, producing a mild fever, runny nose and cough; the cough then typically worsens and can last for two or more months.

A new vaccine in the 1940s sent pertussis cases in this country plummeting to a low of 1,010 in 1976. But the disease roared back in the ’90s. According to the national Centers for Disease Control and Prevention, about 10,000 cases were reported in 2003.

Experts say that number may be low because many cases of pertussis go unrecognized.

Teens and adults almost always recover fully from pertussis, but that’s not the case with infants who have not been vaccinated or who are only partially vaccinated.

So far, few infants have died. Physicians and public-health experts say the number could grow if the problem is not confronted; they believe a yet-to-be-approved booster could help keep the disease in check.

The disease probably has been underestimated for many years, experts say. However, a recent upswing in cases — pertussis outbreaks occur in cycles, with peaks emerging about every three years — has brought new attention.

“The vaccine only lasts a short period of time,” says Dr. James Cherry, a professor of pediatric infectious diseases at UC-Los Angeles and a national authority on childhood vaccines. The vaccine, a combo diphtheria-tetanus-pertussis shot, is given in five doses — usually at 2, 4, 6 and 15 months and at 4 to 6 years.

“The biggest problem is older people taking it (the disease) home to newborns,” Cherry says.

Public-health officials hope they can soon stop the rise of the disease. Two pharmaceutical companies have asked the Food and Drug Administration to approve a diphtheria-tetanus-pertussis booster shot that would confer 10 or so years of extended immunity.

Sanofi Pasteur is seeking approval to sell its booster, Adacel, to people ages 11 to 64. GlaxoSmithKline has asked the FDA to approve its shot, Boostrix, for those 10 to 18.

The FDA is expected to rule on the boosters this spring. Other than the five-dose diphtheria-tetanus-pertussis childhood vaccine, there is no licensed pertussis vaccine for people older than 7.

“This (booster) vaccine has the potential to be really helpful in controlling these outbreaks,” says Dr. Amy Middleman, an assistant professor of pediatrics at Baylor College of Medicine in Houston. “The really important time to cover people is in the adolescent years. That seems to be where the incidence is rising the highest.”

Adults get pertussis, but outbreaks seem most common in teens and young adults who share crowded classrooms and dorms.

Whether older adults also should receive a booster is the subject of much debate. Cherry says his studies have shown that about 13 percent of adults with chronic coughs are actually infected with pertussis. The disease is transmitted by airborne droplets when the infected person coughs or sneezes. If one member of a household is infected, up to 90 percent of the other family members probably will be.

“The majority of infants who get pertussis get it from a family member over the age of 10, and 30 percent to 40 percent get it from [a parent],” Cherry says.

A booster shot may be recommended for teens as well as any adult in contact with infants, such as adults who may have a baby, infant day-care workers and pediatric-health workers.

Doctors also are hoping that heightened public awareness about pertussis will lead to more timely diagnosis and aggressive treatment. Antibiotics, if given early enough, can make the infection less contagious, though they may not alleviate the symptoms.

“What happens with [adults] is that sometimes these people have been coughing for months and may be pretty sick. But adult physicians are not really trained to think about pertussis,” says Hoffman.

Adults who cough for longer than two weeks should be seen by a doctor, Middleman says. Pertussis can be diagnosed with a simple blood test. Adults with coughs should stay away from babies younger than 6 months of age.